1. Field of the Invention:
The invention relates to an apparatus for extracting fluid samples from a selected formation of a subterranean well, and particularly to an apparatus for extracting virgin fluid from the selected formation and transferring such fluid to the well surface without contamination.
2. History of the Prior Art:
It has long been the practice in the drilling of subterranean wells to extract fluid samples from various formations traversed by the well as the drilling proceeds. Fluid samples from any particular selected formation taken under these circumstances is subject to a high degree of contamination by drilling fluid which necessarily has to be present in the well. Accordingly, the prior art apparatus for extracting fluid samples from a selected formation have not been constructed in such manner as to obtain an uncontaminated virgin sample of the fluid actually existing in the formation. When, however, the drilling of the well is substantially completed, and all of the drilling mud has been flushed out of the well bore, the opportunity is present for obtaining a virgin fluid sample from a selected formation in the well. Such sample must be isolated from any contamination by well fluids existing in the annulus above or below the selected formation and from any fluids employed in the operation of the sampling apparatus. Prior art apparatus have not met this criteria.